1. Field of the Invention
One of the aspects of the present invention relates to a belt driving unit that corrects a skew of an endless belt stretched around a plurality of supporting members and to an image forming apparatus including the same.
2. Description of the Related Art
Known image forming apparatuses in the related art are equipped with endless belts, such as an intermediate transfer belt, a fixing belt, and a recording-paper conveying belt, and a belt driving unit for driving such endless belts. The belt driving unit drives the endless belts. Each endless belt is supported by a driving roller and a driven roller, which is rotationally driven by the driving roller.
Ideally, the endless belts are conveyed without skewing in a direction perpendicular to a direction in which the endless belts are conveyed (i.e., a widthwise direction). However, it is known that the endless belts are skewed in the widthwise direction and meander due to various causes, such as the inclinations of the rollers, a difference in tension between the right and left of the endless belts, and external load fluctuations. One example of a technology for correcting the meandering of the endless belts is a technology of inclining a steering roller (for example, refer to Japanese Patent Laid-Open No. 2009-282196).
However, the technology disclosed in Japanese Patent Laid-Open No. 2009-282196 has a problem in that it requires a configuration for inclining the steering roller, which increases the size and cost of the apparatus.
Thus, a technology for correcting the meandering of the endless belts by stretching the endless belts round a plurality of separate driving rollers disposed on the same axis and separately controlling the rotational speeds of the individual rollers has been proposed (for example, refer to Japanese Patent Laid-Open No. 2006-030711).
However, it is difficult for the technology disclosed in Japanese Patent Laid-Open No. 2006-030711 to apply sufficient forces in the widthwise direction of the endless belts even if the plurality of separate driving rollers are driven at different speeds. Therefore, a sufficient widthwise skewing force cannot be applied to the endless belts, and thus, it is difficult to correct the meandering of the endless belts only with this configuration.